Problem description:
Every morning,engine can be started without any problem. Car runs great. When I turn off the engine after about 20 miles high way, then start the engine immediately, it works. However, after about 20 minutes, if I try to start the engine again, it won't work. Then I have to wait for about 4 hours. Then the engine can be started well.

When the engine can not be started, I tried to put the transmission in N position. Nothing happens. There is no sound. I can only see that all the light dim as normal. I changed the battery, positive cable from battery to starter. I checked the alternator as following:

By eyes: I monitored the voltage meter in the panel and found the chargeis a bit more than middle at the begining of driving and then will point to middel after about 10 miles.

By voltage meter: engine stop=12-13v. engine idle@1000rpm=16v. engine idle@2000rpm=17v.

That is my daily problem. But it is headache. I also sent to a local volvo dealer. After charged me $79 checking fee, he told me the answer: he can not figure out the problem and suggest me to buy a new volvo. Jesus, I am still a student.

Please give me some suggestion and let me know what I should try.

Thanks a lot.